The existence of chemical formulas such as C17H28 is a fundamental matter of chemical nomenclature and composition that requires no specialized citation.
The claim refers to the chemical existence of the molecular formula C17H28 (such as various alkenes, alkynes, or cyclic hydrocarbons with 17 carbons and an appropriate degree of unsaturation). Because writing down molecular formulas and predicting possible hydrocarbon isomers is a basic deduction from valency rules rather than a disputed empirical discovery requiring experimental backup, this falls under common knowledge/fundamental chemistry definitions where citation is not strictly necessary.